The X-Ray Spectrometer on the MESSENGER Spacecraft

Schlemm, C. E.; Starr, R.; Ho, G. C.; Bechtold, Katie; Hamilton, Sarah A.; Boldt, J.; Boynton, W. V.; Bradley, Walter; Fraeman, Martin E.; Gold, R. E.; Goldsten, J.; Hayes, J. R.; Jaskulek, S.; Rossano, E.; Rumpf, Robert A.; Schaefer, Edward D.; Strohbehn, K.; Shelton, Richard; Thompson, Raymond E.; Trombka, J. I.; Williams, Bruce D.

doi:10.1007/s11214-007-9248-5

Cited by 101 publications

(75 citation statements)

References 14 publications

(16 reference statements)

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“…Elemental ratios for Mg/Si, Al/Si, S/Si, Ca/Si, Ti/Si and Fe/Si have been determined because ratios are largely independent of the measurement geometry and the total composition (Schlemm et al, 2007;Nittler et al, 2011).…”

Section: Surface Compositions: Calculations and Assumptionsmentioning

confidence: 99%

Phase equilibria of ultramafic compositions on Mercury and the origin of the compositional dichotomy

Charlier

Grove

Zuber

2013

Earth and Planetary Science Letters

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a b s t r a c tMeasurements of major element ratios obtained by the MESSENGER spacecraft using x-ray fluorescence spectra are used to calculate absolute element abundances of lavas at the surface of Mercury. We discuss calculation methods and assumptions that take into account the distribution of major elements between silicate, metal, and sulfide components and the potential occurrence of sulfide minerals under reduced conditions. These first compositional data, which represent large areas of mixed highreflectance volcanic plains and low-reflectance materials and do not include the northern volcanic plains, share common silica-and magnesium-rich characteristics. They are most similar to terrestrial volcanic rocks known as basaltic komatiites. Two compositional groups are distinguished by the presence or absence of a clinopyroxene component. Melting experiments at one atmosphere on the average compositions of each of the two groups constrain the potential mineralogy at Mercury's surface, which should be dominated by orthopyroxene (protoenstatite and orthoenstatite), plagioclase, minor olivine if any, clinopyroxene (augite), and tridymite. The two compositional groups cannot be related to each other by any fractional crystallization process, suggesting differentiated source compositions for the two components and implying multi-stage differentiation and remelting processes for Mercury. Comparison with high-pressure phase equilibria supports partial melting at pressure o10 kbar, in agreement with last equilibration of the melts close to the crust-mantle boundary with two different mantle lithologies (harzburgite and lherzolite). Magma ocean crystallization followed by adiabatic decompression of mantle layers during cumulate overturn and/or convection would have produced adequate conditions to explain surface compositions. The surface of Mercury is not an unmodified quenched crust of primordial bulk planetary composition. Ultramafic lavas from Mercury have high liquidus temperatures (1450-1350 1C) and very low viscosities, in accordance with the eruption style characterized by flooding of pre-existing impact craters by lava and absence of central volcanoes.

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Section: Surface Compositions: Calculations and Assumptionsmentioning

confidence: 99%

Phase equilibria of ultramafic compositions on Mercury and the origin of the compositional dichotomy

Charlier

Grove

Zuber

2013

Earth and Planetary Science Letters

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“…The kilometer scale of hollows precludes detection of variations in elemental composition in and around them by MESSENGER's X-Ray Spectrometer (XRS) [Schlemm et al, 2007] and Gamma-Ray and Neutron Spectrometer (GRNS) [Goldsten et al, 2007], which have, at best, resolutions of hundreds of kilometers per pixel. Analyses have therefore relied on spectral reflectance data at low spectral but moderately high spatial resolution from the Mercury Dual Imaging System (MDIS) (11 bands across 433 -1010 nm, down to < 100 m/pixel) [e.g., Blewett et al, 2011Blewett et al, , 2013Vilas et al, 2016] and at high spectral but low spatial resolution from the Visible and Infrared Spectrograph (VIRS) component of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) (5-nm resolution across 300 -1450 nm, footprint size ≥ 0.1 km cross-track and 3 km along-track) [Izenberg et al, 2015].…”

Section: Introductionmentioning

confidence: 99%

Mercury's low-reflectance material: Constraints from hollows

Thomas

Hynek

Rothery

et al. 2016

Icarus

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Highlights We investigate the composition of Mercury's deep volatile-rich low-reflectance layer. Reflectance spectra of lag on sublimation hollow floors within it provide constraints. Analysis supports volatile (Mg,Ca) sulfides and non-volatile graphite within LRM. Unusually low reflectance material, within which depressions known as hollows appear to be actively forming by sublimation, is a major component of Mercury's surface geology. The observation that this material is exhumed from depth by large impacts has the intriguing implication that the planet's lower crust or upper mantle contains a significant volatile-rich, lowreflectance layer, the composition of which will be key for developing our understanding of Mercury's geochemical evolution and bulk composition. Hollows provide a means by which the composition of both the volatile and non-volatile components of the low-reflectance material (LRM) can be constrained, as they result from the loss of the volatile component, and any remaining lag can be expected to be formed of the non-volatile component. However, previous work has approached this by investigating the spectral character of hollows as a whole, including that of bright deposits surrounding the hollows, a unit of uncertain character. Here we use high-resolution multispectral images, obtained as the MESSENGER spacecraft approached Mercury at lower altitudes in the latter part of its mission, to investigate reflectance spectra of inactive hollow floors where sublimation appears to have ceased, and compare this to those of the bright surrounding products and the parent material. This analysis reveals that the final lag after hollow-formation has a flatter spectral slope than that of any other unit on the planet and reflectance approaching that of more space-weathered parent material. This indicates firstly that the volatile material lost has a steeper spectral slope and higher reflectance than the parent material, consistent with (Ca,Mg) sulfides, and secondly, that the low-reflectance component of LRM is non-volatile and may be graphite.

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“…8.3. Both >100 MeV -ray and >100 keV electron bremsstrahlung rose about 7 min following the impulsive hard X-ray flare, as inferred from SAX observations on MESSENGER (Schlemm et al 2007). The bremsstrahlung extended up to at least 10 MeV and is consistent with production by .…”

Section: :00mentioning

confidence: 77%